Wireless Communication Apparatus, Mobile Wireless Communications Control Method, And Wireless Station

ABSTRACT

A wireless communication apparatus for performing transmission and reception by using a Time Division Duplexing method is disclosed. The wireless communication apparatus includes a receiving part configured to output a timing signal based on a received timing signal, a transmitting part configured to transmit a timing signal based on the timing signal received by the receiving part, a control part configured to increase a reception opportunity for the receiving part to receive the timing signal and decrease a transmission opportunity for the transmitting part to transmit the timing signal as the accuracy of the timing signal received by the receiving part becomes lower.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority ofInternational Patent Application No. 2007-054563 filed on Mar. 8, 2007,the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a wireless communicationapparatus, a mobile wireless data processing apparatus, and a wirelessstation that control transmission/reception periods of wirelesscommunications between plural wireless stations (for example, control byusing TDD (Time Division Duplexing).

BACKGROUND

There are various known methods for communicating between communicationsapparatuses, and various multiplexing communication methods are proposedin response to demands for achieving large capacity transmission.

For example, TDMA (Time Division Multiple Access), FDMA (FrequencyDivision Multiple Access), CSMA (Carrier Sense Multiple Access), andCDMA (Code Division Multiple Access) are known and are also used inwireless communications.

Further, various systems, in combination with the multiplexingcommunication methods, are known for achieving wireless communicationsbetween many mobile stations or between a base station and plural mobilestations.

A mobile phone system may have plural base stations allocated in ascattered manner so that service areas partly overlap each other.Thereby, communications between a mobile phone and other mobile phonesor stationary telephones can be established while the mobile phone isbeing carried on the move, and the base stations can assign channels toeach mobile phone.

Further, there is proposed a control method in which a mobile stationrequests a base station to assign a channel from a shared channel byusing a CSMA/CA method, and the base station performs scheduling oftransmission time by using TDMA (see, for example, Patent Document 1).

Further, there is proposed a system and a method that periodicallydivide a beacon region (where beacon packets are transmitted from pluralmaster stations (stationary stations)), a TDMA region (where specificauthorized stations use bandwidths assigned thereto), and a CSMA region(where competitive access is made) on a time-line and allow selection ofa region enabling bandwidth guarantee (see, for example, Patent Document2).

Patent Document 1: Japanese Laid-Open Patent Publication No. 2002-374265Patent Document 2: Japanese Laid-Open Patent Publication No. 2005-73240

In a case where plural mobile stations perform wireless communicationsdirectly with other mobile stations, communication channels in apredetermined frequency bandwidth are to be assigned in a manner thatthe mobile stations do not interfere with each other.

In a case where a base station (stationary station) has almost all areasas its service areas, the base station (stationary station) can assigncommunication channels to mobile stations and control the communicationchannels. However, in a case where plural base stations are scattered atstrategic locations along a path or the like or where the base stationhas an event site as its service area, a mobile station cannot receivethe service of being assigned a communication channel unless the mobilestation moves to a service area (hot spot) of the base station(s).

Accordingly, wireless communications between mobile stations areperformed by using, for example, a slotted aloha method (in which framesand slots are synchronized between the mobile stations) andnon-colliding communication channels are autonomously selected. Further,the slotted aloha method, for example, is used for establishing multipleaccess among mobile stations whereas the TDD (Time Division Duplexing)method, for example, is used for establishing wireless communicationsbetween mobile stations and base stations.

With this mobile wireless system, a mobile station determines the timingfor performing transmission according to the TDD slot timing of a basestation when the mobile station approaches the base station andcommunicates in synchronization with the TDD slot timing of the basestation when the mobile station communicates with the base station.

However, in a case where no base station exists in the vicinity of amobile station, the mobile station, unlike using a cellular wirelessmethod in which the mobile station can obtain a slot timing signal froma base station, is required to continue to autonomously obtain thetiming for synchronizing with the base station.

Therefore, there is conceived a synchronizing method in which accuratetime data are obtained from a GPS (Global Positioning System) forsynchronizing with the slot timing. In order to continue obtaining timedata from radio-waves received from a GPS satellite, it is necessary tocontinue receiving radio-waves constantly from four or more GPSsatellites in order to receive the time data.

In a case where the mobile station is located in an area where thestatus of receiving radio-waves from the GPS satellites isunsatisfactory, it is difficult for the mobile station to obtain timedata from the radio-waves of the GPS satellites. Therefore, in somecases, it may be difficult to autonomously continue synchronization.

Further, in a case where no base station exists in the vicinity of amobile station and the status of received radio-waves from GPSsatellites is unsatisfactory, it is possible to perform wirelesscommunications by using, for example, the slotted aloha method.

However, in order to efficiently perform wireless communications bymaking the length of time of a time slot (time slot length) used by theslotted aloha method substantially equal to the length of time of a timeslot (time slot length) designated by TDD slot timing used by the basestation according to the TDD method, it is necessary to receiveradio-waves from GPS satellites and continue maintaining slotsynchronization by obtaining accurate time data from the radio-waves.

In this case, it is often difficult for the mobile station to constantlyobtain accurate time data. Accordingly, continuing to maintainsynchronization of high accuracy is difficult, and wirelesscommunications of other mobile stations may be obstructed by suchdifficulty.

SUMMARY

In order to achieve the object, there is provided a wirelesscommunication apparatus for performing transmission and reception byusing a Time Division Duplexing method, the wireless communicationapparatus including: a receiving part configured to output a timingsignal based on a received timing signal; a transmitting part configuredto transmit a timing signal based on the timing signal received by thereceiving part; a control part configured to increase a receptionopportunity for the receiving part to receive the timing signal anddecrease a transmission opportunity for the transmitting part totransmit the timing signal as the accuracy of the timing signal receivedby the receiving part becomes lower.

Further, in order to achieve the object, there is provided a wirelesscommunication apparatus for performing transmission and reception byusing a Time Division Duplexing method, the wireless communicationapparatus including: a receiving part configured to output a timingsignal based on a received timing signal; a transmitting part configuredto transmit a timing signal based on the timing signal received by thereceiving part; a control part configured to decrease a receptionopportunity for the receiving part to receive the timing signal andincrease a transmission opportunity for the transmitting part totransmit the timing signal as the accuracy of the timing signal receivedby the receiving part becomes lower.

Further, in order to achieve the object, there is provided a mobilewireless communications control method for controllingtransmission/reception periods of wireless communications among aplurality of wireless stations by using a Time Division Duplexingmethod, the mobile wireless communications control method including thesteps of: obtaining same time data of high accuracy from outside thewireless station; receiving a signal frame including at least asynchronization signal indicating a timing transmitted from anotherstation and sub-data indicating a synchronization status; generating asynchronization signal according to the time data, the synchronizationsignal obtained from the other station, or a synchronization signalbased on a self-propelled oscillation; storing sub-data indicating thesynchronization status of the wireless station itself; transmitting asignal frame including the synchronization signal and the sub-data;initializing the synchronization signal and the sub-data of the wirelessstation itself when time data are obtained in the time data obtainingstep; and updating the synchronization signal and the sub-data of thewireless station itself according to a result of comparing the sub-datareceived from the other station with stored sub-data of the wirelessstation itself.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a configuration of a wireless stationaccording to an embodiment of the present invention;

FIG. 2 is a diagram illustrating an embodiment of a frame format of awireless frame;

FIG. 3 is a flowchart of an operation executed by a mobile station;

FIG. 4 is a diagram for explaining the number of hops of each mobilestation of a wireless mobile communication control method according toan embodiment of the present invention;

FIG. 5 is another diagram for explaining the number of hops of eachmobile station of a wireless mobile communication control methodaccording to an embodiment of the present invention;

FIG. 6 is a diagram for explaining a system focusing on expansion of asubordinate synchronization area according to an embodiment of thepresent invention; and

FIGS. 7A and 7B are diagrams for describing a configuration of asub-data part of each embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Next, embodiments of the present invention are described with referenceto the drawings.

With the below-described embodiments of a wireless communicationapparatus, synchronization in accordance with high accuracysynchronization signals can be achieved. Furthermore, high accuracysynchronization can be achieved among plural wireless stations.Furthermore, wireless resources can be efficiently used.

<Configuration of Mobile Station and Base Station>

FIG. 1 is a block diagram illustrating a wireless station 10 accordingto an embodiment of the present invention. Although this wirelessstation 10 is illustrated having a configuration of a mobile station,the configuration may be applied not only to a mobile station but alsoto a base station.

In FIG. 1, a time data reception circuit 11 has a calculating functionin which high accuracy time data are obtained by catching transmissionsof a group of GPS satellites with an antenna 11 a.

The time data reception circuit 11 catches the group of GPS satellites.For example, the time data reception circuit 11 receives signalsincluding time data transmitted from four GPS satellites and performsslight adjustment of an inside oscillator, to thereby output highaccuracy timing signals synchronized with the GPS satellites.

The time data reception circuit 11 outputs the high accuracy timingsignals to a synchronization determining circuit 12 and a selector 13.It is to be noted that, the outputting of high accuracy timing signalsis stopped in a case where the high accuracy timing signals cannot beoutput due to a decrease in the number of GPS satellites that can becaught.

The synchronization determining circuit 12 determines whether highaccuracy timing signals have been obtained from the time data receptioncircuit 11. For example, in a case where timing signals are output fromthe synchronization determining circuit 12, the synchronizationdetermining circuit 12 determines that timing signals of high accuracyhave been obtained. In the case where high accuracy timing signals areobtained (e.g., a case where time data are obtained by catching four GPSsatellites), the selector 13 is controlled to select the timing signalsoutput from the time data reception circuit 11. On the other hand, in acase where high accuracy timing signals are not obtained, the selector13 is controlled to select synchronization signals (signals having lessaccuracy compared to timing signals from the time data reception circuit11) provided from a switch 23. Further, the synchronization determiningcircuit 12 reports the obtaining of the high accuracy timing signals toa transmission timing scheduler 14 and a counter 24 and initializes astoring circuit 26 by storing a hop count of “0” in the storing circuit26.

Because the selector 13 receives a report from the synchronizationdetermining circuit 12 in a case where high accuracy timing signals havebeen obtained, the selector 13 selects the timing signals from the timedata reception circuit 11 when receiving the report from thesynchronization determining circuit 12. Other than such a case, theselector 13 selects synchronization signals from the switch 23. Theselector 13 transmits the selected signals to a reference timinggenerating circuit 15.

The reference timing generating circuit 15 has a self-propelled clockoscillator. In order to generate a reference timing signal indicatingthe beginning of a frame in synchronization with the high accuracytiming signals or the synchronization signals input to the referencetiming generating circuit 15, the reference timing generating circuit 15resets the clock oscillator and the reference timing signal. In a casewhere neither the high accuracy timing signals nor the synchronizationsignals are input, the reference timing generating circuit 15 generatesthe reference timing signal by counting the output clock of theself-propelled clock oscillator. The reference timing signal istransmitted to a transmission/reception timing generating circuit 16 anda synchronization signal transmission/reception circuit 17.

The transmission timing scheduler 14 obtains a report indicating whetherhigh accuracy timing signals have been obtained, a report indicatingreception of synchronization signals, and a report indicating update ofthe hop count along with obtaining the hop count stored in the storingcircuit 26. The transmission timing scheduler 14 determines the timingfor transmitting a wireless frame (transmission interval) according to,for example, the hop count stored in the storing circuit 26 and reportsthe determined timing to the transmission/reception timing generatingcircuit 16.

Based on the reference timing signal from the reference timing signalgenerating circuit 15 and the transmission timing (transmissioninterval) from the transmission timing scheduler 14, thetransmission/reception timing generating circuit 16 generatestransmission/reception timing signals indicating the timing fortransmitting/receiving a synchronization signal, sub-data (hop count),and a slot of its own station and transmits the transmission/receptiontiming signal indicating the synchronization signal to thesynchronization signal transmission/reception circuit 17, thetransmission/reception timing signal indicating the sub-data to asub-data transmission/reception circuit 18, and thetransmission/reception timing signal indicating a main datatransmission/reception circuit 19.

A multiplexing/demultiplexing circuit (MUX/DMUX) 21 separates receivedwireless frames received by the antenna 21 a and transmits the separatedframes to the synchronization signal transmission/reception circuit 17,the sub-data transmission/reception circuit 18, and the main datatransmission/reception circuit 19. The multiplexing/demultiplexingcircuit (MUX/DMUX) 21 also multiplexes transmission signals from thesynchronization signal transmission/reception circuit 17, the sub-datatransmission/reception circuit 18, and the main datatransmission/reception circuit 19 as wireless frames and transmits themultiplexed wireless frames to the antenna 21 a.

FIG. 2 illustrates a frame format of an embodiment of a wireless frame.In FIG. 2, the horizontal axis represents time and the vertical axisrepresents frequency. For example, the wireless frame(s) istransmitted/received in frame periods of several milliseconds. A singlewireless frame includes a synchronization signal part, a sub-data part(to which a hop count is set), and a main data part (including n slotsbeing set with communication data that are to be reported from eachmobile station to a corresponding mobile station).

In a case where a mobile station has communication data to betransmitted, the mobile station selects one of the n slots and sets thecommunication data to the selected slot (or a slot assigned to themobile station). In a case where the mobile station has no communicationdata to be transmitted, the mobile station does not need to set maindata. Thus, in this case, the mobile station may transmit a wirelessframe only with a synchronization signal part and a sub-data part towhich a hop count is set. Normally, a base station also transmits awireless frame only with a synchronization signal part and a sub-datapart to which a hop count is set.

The synchronization signal transmission/reception circuit 17 is fortransmitting/receiving synchronization signal. The synchronizationsignal transmission/reception circuit 17 supplies receivedsynchronization signals to a synchronization signal receptiondetermining circuit 22 and the switch 23. The synchronization signalreception determining circuit 22 determines reception of asynchronization signal. In a case where the synchronization signalreception determining circuit 22 determines that a synchronizationsignal is received, the synchronization signal reception determiningcircuit 22 reports the reception of the synchronization signal to thebelow-described comparing circuit 27. In addition, the synchronizationsignal reception determining circuit 22 generates a signal for reportingthe reception of the synchronization signal and transmits the signal tothe transmission timing scheduler 14 and the counter 24.

The counter 24 is reset when receiving a signal indicating that a highaccuracy timing signal has been obtained or a signal indicating that asynchronization signal has been received. Then, the counter 24 beginscounting, for example, clock signals from the reference timinggenerating circuit 15, then generates a timeout signal after apredetermined time elapses, and then transmits the timeout signal to anupdate determining circuit 25.

In other words, in a case where the supply of high accuracy timingsignals or synchronization signals is stopped, the timing signalgenerated by the reference timing generating circuit 15 becomes aself-propelled timing signal having low accuracy. Accordingly, theupdate determining circuit 25 is instructed to store “0xFFFF” (“0x”representing a hexadecimal digit”), indicating that the accuracy of thetiming signal is lowest, in the storing circuit 26.

The predetermined time is determined according to the accuracy of theclock oscillator of the reference timing generating circuit 15. Thepredetermined time is preferred to be approximately a few hours wherethe accuracy of the clock oscillator is high and approximately a fewminutes to a few ten minutes where the accuracy of the clock oscillatoris low.

A sub-data transmission/reception circuit 18 transmits/receives sub-data(hop count) and supplies received hop counts to the storing circuit 26and the comparing circuit 27. The hop count of the mobile station 10itself is stored in the storing circuit 26. The hop count stored in thestoring circuit 26 is transmitted to the comparing circuit 27 and thetransmission timing scheduler 14. Further, “1” is added to a hop countby an adding circuit 28. Then, the hop count with “1” added istransmitted as sub-data to the sub-data transmission/reception circuit18.

The adding circuit 28, however, does not add “1” in a case where the hopcount stored in the storing circuit 26 is a first characteristic value“0” or a second characteristic value “0xFFFF”. This is because the firstcharacteristic value “0” indicates that a high accuracy timing signalhas been obtained by the time data reception circuit 11 of the mobilestation 10 itself and has no reason for a signal from another station tobe hopped.

The comparing circuit 27 compares the hop count stored in the storingcircuit 26 and the hop count newly received by the sub-datatransmission/reception circuit 18 and supplies the comparison result tothe update determining circuit 25. In a case where the newly receivedhop count is equal to or less than (or less than) the hop count storedin the storing circuit 26 or in a case where a timeout signal isreceived from the counter 24, the update determining circuit 25generates an update control signal to cause the storing circuit 26 toupdate the hop count of the mobile station 10 itself by storing thereceived hop count and closes the switch 23 so that synchronizationsignals received in the synchronization signal transmission/receptioncircuit 17 are transmitted to the selector 13 in accordance with theupdated hop count.

Accordingly, when the synchronization signal transmission/receptioncircuit 17 first receives a synchronization signal having a high hopcount in a situation where GPS satellite signals cannot be caught, thefirst received synchronization signal is transmitted to the referencetiming generating circuit 15. However, in a case where a subsequentsynchronization signal is received immediately after receiving the firstreceived synchronization signal and a relatively low hop count isdetected from the subsequent synchronization signal, the subsequentsynchronization signal can be transmitted to the reference timinggenerating circuit 15 after the first received synchronization signal istransmitted to the reference timing generating circuit 15 because thefirst received synchronization signal has low accuracy.

Further, the update determining circuit 25 transmits the update controlsignal to the transmission timing scheduler 14 to cause the transmissiontiming scheduler to reschedule the transmission timing.

The main data transmission/reception circuit 19 is fortransmitting/receiving main data.

The main data transmission/reception circuit 19 transmits received maindata to a transmission/reception data processing circuit 29.

The transmission/reception data processing circuit 29 processes thereceived main data. In addition, the transmission/reception dataprocessing circuit 29 transmits main data to be transmitted to otherstations to the main data transmission/reception circuit 19.

The transmission/reception data processing circuit 29 may report theexistence of main data to be transmitted to the transmission timingscheduler 14. The transmission timing scheduler 14 may determine thetransmission timing (transmission interval) according to the existingmain data to be transmitted.

<Operation Executed by Wireless Station>

FIG. 3 is a flowchart illustrating an operation executed by the wirelessstation 10. In Step S10 of FIG. 3, the synchronization determiningcircuit 12 determines whether a high accuracy timing signal is obtained.In a case where a high accuracy timing signal is obtained, a hop count“0” is stored in the storing circuit 26 and a wireless frame includingthe stored hop count “0” is transmitted as sub-data (hop count) in StepS11.

In a case where the hop count is “0”, no addition is performed in theadding circuit 28. In a case where a high accuracy timing signal is notobtained, the synchronization signal reception determining circuit 22determines reception of a synchronization signal in Step S12.

In a case where a synchronization signal is received, the comparingcircuit 27 compares the hop count stored in the storing circuit 26 witha hop count newly received, along with the reception of thesynchronization signal, by the sub-data transmission/reception circuit18 and determines whether the received hop count is equal to or lessthan the stored hop count in Step S13. Alternatively, it may bedetermined whether the received hop count is less than the stored hopcount.

In a case where the received hop count is equal to or less than thestored hop count, the update determining circuit 25 updates the hopcount by storing the received hop count in the storing circuit 26 andtransmits a wireless frame, having “1” added to the stored hop count bythe adding circuit 28, as sub-data (hop count).

On the other hand, in a case where the received hop count is greaterthan the stored hop count in Step S13 or where no synchronization signalis received in Step S12, the operation proceeds to Step S15 in which theupdate determining circuit 25 determines whether a timeout signal istransmitted from the counter 24.

In a case where no timeout signal is transmitted, the operation proceedsto Step S16 in which the self-propelled reference timing generatingcircuit 15 generates a reference timing signal and transmits a wirelessframe, having “1” added to the stored hop count by the adding circuit28, as sub-data (hop count).

In a case where a timeout signal is transmitted, the operation proceedsto Step S17 in which the self-propelled reference timing generatingcircuit 15 generates a reference timing signal, causes the storingcircuit 26 to store a second characteristic value “0xFFFF”, andtransmits a wireless frame including the characteristic value “0xFFFF”as sub-data (hop count). In a case where the hop count is “0xFFFF”, noaddition is performed by the adding circuit 28.

<Hop Count of Each Mobile Station>

FIGS. 4 and 5 are drawings for describing the hop count of each mobilestation of a mobile wireless communication control method according toan embodiment of the present invention.

In FIG. 4, a mobile station 40 is in a GPS asynchronous state in whichhigh accuracy timing signals cannot be obtained from a GPS satellite.The mobile station 40 receives a wireless frame transmitted from a basestation 44 and a wireless frame transmitted from a mobile station 41.Because the base station 44 is synchronous with the GPS satellite, awave clock, or a clock based on a high accuracy frequency source, thebase station 44 transmits a wireless frame having a hop count of “0”.Further, the mobile station 41 transmits a wireless frame having a hopcount of “2”.

In other words, because the mobile station 40 is receiving a wirelessframe having a hop count “0” and a wireless frame having a hop count“2”, the mobile station 40 subordinately synchronizes with the wirelessframe having a smaller hop count of “0” and transmits a wireless framehaving a hop count of “1”.

The mobile station 41 is in a GPS asynchronous state in which the mobilestation 41 receives a wireless frame, transmitted from the mobilestation 40, having a hop count “1” and a wireless frame, transmittedfrom the mobile station 42, having a hop count “1”. Therefore, themobile station 41 subordinately synchronizes with the wireless frame,transmitted from the mobile station 40, having a hop count “1” andtransmits a wireless frame having a hop count “2”.

The mobile station 42 is in a GPS asynchronous state in which the mobilestation 42 receives a wireless frame, transmitted from a mobile station43, having a hop count of “0” and a wireless frame, transmitted from themobile station 41, having a hop count of “2”. Therefore, the mobilestation 42 subordinately synchronizes with the wireless frame,transmitted from the mobile station 43, having a hop count of “0” andtransmits a wireless frame having a hop count “1”.

Because the mobile station 43 is in a GPS synchronous state in which themobile station 43 can obtain high accuracy timing signals from the GPSsatellite 45, the mobile station 43 transmits a wireless frame having ahop count of “0”.

In FIG. 5, the mobile station 40 is in a GPS asynchronous state in whichthe mobile station 40 receives a wireless frame, transmitted from themobile station 41, having a hop count of “0xFFFF”. Therefore, the mobilestation 41 subordinately synchronizes with the wireless frame having ahop count of “0xFFFF” and transmits a wireless frame having a hop countof “0xFFFF”.

The mobile station 42 is in a GPS asynchronous state in which the mobilestation 42 receives a wireless frame, transmitted from the mobilestation 41, having a hop count of “0xFFFF”. Therefore, the mobilestation 42 subordinately synchronizes with the wireless frame having ahop count of “0xFFFF” and transmits a wireless frame having a hop countof “0xFFFF”.

The mobile station 43 is in a GPS asynchronous state and receives nowireless frames from other mobile stations. Therefore, the mobilestation 43 synchronizes with a reference timing signal generated fromthe self-propelled reference timing generating circuit 15 and transmitsa wireless frame having a hop count of “0xFFFF”.

<Transmission Timing of Each Mobile Station>

Each mobile station achieves duplex communications of synchronizationsignals and sub-data (hop count) using wireless frames. The timing ofthe communications is determined according to the hop count of thewireless frame to be transmitted, that is, the hop count output from theadding circuit 28. The hop count stored in the storing circuit 26 may beused instead of the hop count output by the adding circuit 28.

In a case where the hop count is “0”, there is no need for a mobilestation to receive synchronization signals. Therefore, the mobilestation 42 transmits a synchronization signal and sub-data, for example,every single frame. In a case where the hop count is equal to or greaterthan “1”, it is necessary for the mobile station to transmit asynchronization signal while monitoring synchronization signals of otherstations. Therefore, the mobile station repeats transmission andreception in a predetermined frame period (e.g., once every two frames).This period is controlled according to the hop count. Typically, in acase where “M” represents a transmission period when the hop count is“0” and “N” represents a transmission period when the hop count is equalto or greater than “1”, “N” is set to be greater than “M” (M<N).

In other words, with a mobile station that performs transmission andreception by using a TDD method, in a case of obtaining reference timingsignals from the time data reception circuit 11 and the synchronizationsignal transmission/reception circuit 17 and transmittingsynchronization timing signals from the synchronization signaltransmission/reception circuit 17 according to the obtained referencetiming signals, the opportunity for allowing the synchronization signaltransmission/reception circuit 17 to receive synchronization timingsignals increases and the opportunity for allowing the synchronizationsignal transmission/reception circuit 17 to transmit synchronizationtiming signals decreases as the accuracy of the received synchronizationtiming signal becomes lower. The control of the transmission opportunityand the reception opportunity may not only be performed temporarily butalso continuously.

In a case of a system laying weight on expansion of master/slavesynchronization areas, a mobile station having high reliability laysweight on transmission of synchronization signals. Therefore, a mobilestation having a hop count “1” transmits wireless frames (including asynchronization signal part) in odd number frames and receives wirelessframes (including a synchronization signal part) in even number frames.In other words, the mobile station performs communications by switchingbetween transmission and reception of wireless frames in 1 frameperiods.

A mobile station having a hop count “2” switches between transmissionand reception of wireless frames, for example, by transmitting wirelessframes including synchronization signals in a first frame and receivingwireless frame in second and third frames. Further, a mobile stationhaving a hop count “3” switches between transmission and reception ofwireless frames, for example, by transmitting wireless frames includingsynchronization signals in a first frame and receiving wireless framesin second, third, and fourth frames. Alternatively, the switchingbetween transmission and reception of wireless frames may be performedin 2 frame periods.

In this embodiment, the opportunity for transmission is set to begreater than the opportunity for reception in a case where high accuracytiming signals are obtained. Alternatively, the opportunity fortransmission may be set to be greater than the opportunity for receptionin a case where the amount of data to be transmitted is large.Accordingly, the opportunity for transmission can be increased formobile stations having large amounts of data, and the opportunity forreception by other mobile stations increases. Accordingly, theprobability for success of reception increases.

In this case, by intentionally setting the hop count to a low value of,for example, “0” or “1”, it becomes easier to be used as a timingsignal. Accordingly, increase in the probability of successful receptioncan be expected. Instead of setting the hop count to a predeterminedvalue (e.g., “0” or “1”), transmission may be performed by subtracting apredetermined value (e.g., “1”, “2”, or “3”).

Alternatively, in a case where “M” represents a transmission period whenthe hop count is “0” and “N” represents a transmission period when thehop count is equal to or greater than “1”, “N” is set to be less than“M” (M>N). This is effective for a case where weight is placed onimproving reliability.

In such a system placing weight on improving reliability, the greaterthe weight that is placed on reception of wireless frames, the higherthe reliability of the mobile station. Thus, wireless frames equivalentto the number of hop counts are transmitted with respect to reception ofa wireless frame of a single frame. In terms of mobile stations having ahop count of “0” or “1” the transmission periods are the same as theexpanding of the master/slave synchronization area.

A mobile station having a hop count “2” switches between transmissionand reception of wireless frames, for example, by transmitting wirelessframes including synchronization signals in first and second frames andreceiving a wireless frame in a third frame. Further, a mobile stationhaving a hop count “3” switches between transmission and reception ofwireless frames, for example, by transmitting wireless frames includingsynchronization signals in first, second, and third frames and receivinga wireless frame in a fourth frame. Alternatively, the switching betweentransmission and reception of wireless frames may be performed in 2frame periods.

Whether to use a system laying weight on the expansion of master/slaveareas or a system laying weight on improvement of reliability depends onthe application used for the system. The proportion between transmissionof wireless frames and reception of wireless frames may not only bedetermined in proportion with the hop count. For example, the proportionbetween transmission of wireless frames and reception of wireless framesmay be determined according to a weighted hop count or according to agiven function having the hop count as a variable.

FIG. 6 is a schematic diagram for describing a transmission timing ofeach mobile station in a system laying weight on expanding themaster/slave area according to an embodiment of the present invention.In FIG. 6, each mobile station 40-43 is in the same state as thoseillustrated in FIG. 4. In this embodiment, the mobile station 40transmits a wireless frame having a hop count “1”, and the mobilestation 43 transmits a wireless frame having a hop count “0”.

Because the hop count is “1” for each of the mobile stations 40, 42, thetransmission timing scheduler 14 of each mobile station 40, 42 transmitswireless frames in odd number frames and receives wireless frames ineven number frames.

Because the hop count is “2” for the mobile station 41, the timingscheduler 14 of the mobile station 41 transmits wireless frames in thefirst frame and receives wireless frames in second and third frames.Because the hop count is “0” for the mobile station 43, the timingscheduler 14 of the mobile station 43 transmits wireless signals inevery frame.

<Transmission Method of Sub-Data>

As illustrated in FIG. 7A, the sub-data part of FIG. 2 may be configuredto indicate hop counts “1” through “m” by making one or “i” (“i” beingan integer equal to or greater than 2) carriers to correspond to asingle hop count (value of hop count). As illustrated in FIG. 7B, thesub-data part may be configured to indicate hop counts “1” through “m”by dividing the sub-data part into “m” time slots and making one timeslot number correspond to a single hop count (value of hop count).Further, the sub-data part may be configured to indicate the value ofhop counts according to the combination of the above-described carriersand time slots.

In a case of performing operations using the configurations illustratedin FIG. 7A or FIG. 7B, it is necessary for the sub-datatransmission/reception circuit 18 to supply hop counts to thesynchronization signal transmission/reception circuit 17.

Further, in order to efficiently transmit sub-data (i.e. hop count), apreamble may be used as the synchronization signal part of FIG. 2 asdescribed in, for example, WiMAX (Worldwide Interoperability forMicrowave Access) of IEEE 802.16e. Because the preamble has an index andthe code pattern of the preamble is different depending on the indexnumber of the preamble, the index can be used to select a preamblehaving an index number matching the number of hop counts. In this case,the sub-data part of FIG. 2 can be eliminated because hop counts can bereceived/transmitted with the synchronization signal part (preamble) ofFIG. 2.

According to related art examples where a mobile station cannot obtainhigh accuracy timing signals or where the mobile station cannotsynchronize with a base station, the slot timings of wireless framesamong mobile stations become asynchronous and result in increase ofcommunication interference among mobile stations. However, with theabove-described embodiments of the present invention, mobile stationscan subordinately synchronize with mobile stations receiving highaccuracy GPS timing signals or synchronization signals of a basestation, to thereby achieve a pseudo-expansion of the synchronizationarea. Further, with the sub-data (hop count of subordinatesynchronization), mobile stations can subordinately synchronize with asynchronization source with higher accuracy. Thus, synchronization amongplural wireless stations can be continued and wireless resources can beused efficiently.

1. A wireless communication apparatus for performing transmission andreception by using a Time Division Duplexing method, the wirelesscommunication apparatus comprising: a receiving part configured tooutput a timing signal based on a received timing signal; a transmittingpart configured to transmit a timing signal based on the timing signalreceived by the receiving part; a control part configured to increase areception opportunity for the receiving part to receive the timingsignal and decrease a transmission opportunity for the transmitting partto transmit the timing signal as the accuracy of the timing signalreceived by the receiving part becomes lower.
 2. A wirelesscommunication apparatus for performing transmission and reception byusing a Time Division Duplexing method, the wireless communicationapparatus comprising: a receiving part configured to output a timingsignal based on a received timing signal; a transmitting part configuredto transmit a timing signal based on the timing signal received by thereceiving part; a control part configured to decrease a receptionopportunity for the receiving part to receive the timing signal andincrease a transmission opportunity for the transmitting part totransmit the timing signal as the accuracy of the timing signal receivedby the receiving part becomes lower.
 3. A mobile wireless communicationscontrol method for controlling transmission/reception periods ofwireless communications among a plurality of wireless stations by usinga Time Division Duplexing method, the mobile wireless communicationscontrol method comprising: obtaining same time data of high accuracyfrom outside the wireless station; receiving a signal frame including atleast a synchronization signal indicating a timing transmitted fromanother station and sub-data indicating a synchronization status;generating a synchronization signal according to the time data, thesynchronization signal obtained from the other station, or asynchronization signal based on a self-propelled oscillation; storingsub-data indicating the synchronization status of the wireless stationitself; transmitting a signal frame including the synchronization signaland the sub-data; initializing the synchronization signal and thesub-data of the wireless station itself when time data are obtained inthe time data obtaining; and updating the synchronization signal and thesub-data of the wireless station itself according to a result ofcomparing the sub-data received from the other station with storedsub-data of the wireless station itself.
 4. A wireless station of amobile wireless communications system for controllingtransmission/reception periods of wireless communications among aplurality of the wireless stations by using a Time Division Duplexingmethod, the wireless station comprising: an obtaining part configured toobtain same time data of high accuracy from outside the wirelessstation; a receiving part configured to receive a signal frame includingat least a synchronization signal indicating a timing transmitted fromanother station and sub-data indicating a synchronization status; asynchronization generating part configured to generate a synchronizationsignal according to the time data, the synchronization signal obtainedfrom the other station, or a synchronization signal based on aself-propelled oscillation; a storing part configured to store sub-dataindicating the synchronization status of the wireless station itself; atransmitting part configured to transmit a signal frame including thesynchronization signal and the sub-data; an initializing part configuredto initialize the synchronization signal and the sub-data of thewireless station itself when time data are obtained by the obtainingpart; and an updating part configured to update the synchronizationsignal and the weight of the sub-data of the wireless station itselfaccording to a result of comparing the weight of the sub-data receivedfrom the other station with the weight of the stored sub-data of thewireless station itself.
 5. The wireless station as claimed in claim 4,wherein the initializing part is configured to cause the synchronizationgenerating part to generate a synchronization signal based on theobtained time data and cause the storing part to store a firstcharacteristic value as the sub-data when the time data obtaining partobtains the time data.
 6. The wireless station as claimed in claim 4,wherein the updating part is configured to cause the synchronizationgenerating part to generate a synchronization signal received from theother station and cause the storing part to store the sub-data receivedfrom the other station when the weight of the sub-data received from theother station is equal to or less than the weight of the sub-data of thewireless station itself.
 7. The wireless station as claimed in claim 5,wherein the updating part is configured to cause the storing part tostore a second characteristic value as the sub-data when a predeterminedtime elapses after the obtaining part obtains the time data or after thereceiving part receives the synchronization signal.
 8. The wirelessstation as claimed in claim 4, further comprising: a transmissioninterval determining part configured to determine an interval fortransmitting a signal frame including at least the synchronizationsignal and the sub-data according to the weight of the sub-data.
 9. Thewireless station as claimed in claim 4, further comprising: atransmission interval determining part configured to determine aninterval for transmitting a signal frame including at least thesynchronization signal and the sub-data according to data amount of maindata to be transmitted with the signal frame.
 10. The wireless stationas claimed in claim 4, wherein, in the signal frame, a single code of acode string having low correlation is transmitted as a synchronizationsignal and a number of the code is set to correspond to sub-data. 11.The wireless station as claimed in claim 4, further comprising: a weightadjusting part configured to change the weight of the sub-data stored inthe storing part and supply the sub-data to the transmitting part. 12.The wireless station as claimed in claim 4, wherein the updating part isconfigured to cause the synchronization generating part to generate asynchronization signal based on a synchronization signal from aself-propelled oscillation and cause the storing part to store sub-datawhen the weight of the sub-data received from the other station is equalto or greater than the weight of the sub-data of the wireless stationitself.
 13. The wireless station as claimed in claim 4, wherein thesub-data included in the signal frame is transmitted by one or morecarriers corresponding to the weight of the sub-data.
 14. The wirelessstation as claimed in claim 4, wherein the sub-data included in thesignal frame is transmitted in one or more divided time slotscorresponding to the weight of the sub-data.
 15. The wireless station asclaimed in claim 4, wherein the sub-data included in the signal frame istransmitted by one or more carriers corresponding to the weight of thesub-data and transmitted in one or more divided time slots correspondingto the weight of the sub-data.